The goal for phase I is to establish, as a model, an immunometric assay for testosterone and achieve, via a highly specific monoclonal antibody, (MAb) an analytical accuracy superior to the commercial kits currently available. The key aspect is to obtain an MAb with the necessary specificity and affinity. Immunoassays currently available suffer from overestimation of the steroid concentration in serum, probably due to an insufficient specificity of the antibody. A 15 carboxymethyl derivation of testosterone coupled to KLH used as an antigen should elicit a MAb with the requisit specificity. The specificity of the MAb selected will be determined assaying crossreactivity with other steroids and testing with serum samples containing chemically determined amounts of steroid. After selection of a highly specific MAb, an immunometric assay utilizing a fluoresant end point will be developed for commercial application.